Carburetor



Dec. 1945- I H. F. TWYMAN I 2,391,755

GARBURETOR Filed May 11, 1943 IN V EN TOR. 'HAEoLo I? TWYMM' PatentedDec. 25, 1945 CABBURETOR Harold F. Twyman, Dayton, Ohio, assignor toChandler-Evans Corporation, South Meriden, Conn., a corporation ofDelaware Application May 11, 1943, Serial No. 486,599

11 Claims.

The present invention relates to carburetors, and particularly tocarburetors adaptedfor use on aircraft, wherein the air and fuelsupplied to the engine are proportioned in a definite ratio to insureoptimum combustion of the fuel in the engine.

In such carburetors, the quantity of air flowing through the carburetoris commonly measured by a Venturi meter or other suitable flow meter,and a force developed by the meter in proportion to the air flow is usedto operate a valve which controls the fuel flow.

It is an object of the present invention to provide, in a carburetor ofthe type described, improved means for producing a metering forceproportional to the flow of air entering the carburetor. I

Another object of the present invention is to provide improved means formeasuring the air flow through a large air passage, wherein the meteringforce produced is representative of the average velocity of the fluidflowing through the entire cross section of the passage.

A further object of the present invention is to provide an improvedVenturi meter, wherein the force developed by the meter is amplified bya boost Venturi meter which is enclosed so as to be entirely separatefrom the main air passage.

A further object of the invention is to provide flow measuring meansincluding improved means for compensating the flow measurement for thepressure and temperature of the fluid being measured so as to produce ametering force proportional to the mass of fiuidbeing measured.

A further object of the invention is to provide improved flow measuringmeans of the type described, wherein a .boost Venturi meter is connectedin a passage between the intake and the throat of a main Venturi, andwherein a Valve responsive to the pressure and temperature of theflowing fluid is used to control the flow thru the boost Venturi so thatits velocity is a measure of the mass of airpassing thru the mainVenturi.

Other objects and advantages of the present invention will becomeapparent from a consideration of the appended specification, claims, anddrawing, in which the single figure represents diagrammatically anaircraft carburetor and controlling devices therefor embodying theprinciples of my invention.

Referring now to the drawing, there is shown at the main body portion ofan aircraft carburetor including a main air passage l I, through whichthe air flows from an entrance [2 to an outlet l3 which connects, bymeans not shown,

to the intake of a supercharger by which the air is forced into theengine under pressure.

The fuel supply for the engine comes from a pump or other source of fuelunder pressure, and passes through a conduit M, a vapor trap IS, aconduit I6, a fuel regulator unit H, a conduit l8, 2. second vapor trap20, a mixture control unit 21; a jet system generally indicated at 22,-a. conduit 23, an idling control 24, a conduit 25,. a pressure regulator26, and a passage 21 to a fuel injection unit, not shown. The fuelinjection unit may preferably be of the type known as a spinnerinjector, wherein the fuel is introduced into the air stream throughsuitable orifices in the rotor of the supercharger.

The carburetor l0 may be of the rectangular type shown in the Jcopendingapplication of Milton E. Chandler, Serial 406,776, filed August 14,1941, now Patent No. 2,361,993, issued Nov. 7, 1944. Nearthe airentrance l2 of the carburetor a plurality of impact tubes 30 projectinto the air stream, with their ends open in a direction to receive thedynamic pressure of the air flowing into the carburetor. These impacttubes open into a passage 3| which interconnects all the impact tubes,and is commonly termed a vent ring. Passages 32 connect the vent rings3| with a chamber 33. A boost Venturi 34 is mounted so that its entranceis in communication with the chamber 33. The discharge end of the boostVenturi is connected thru a valve 35 with a chamber 36 within a housing3'1. The interior of chamber 36 communicates through a conduit 38withthe interiors of a plurality of parallel hollow Venturi members 40which are located in the air passage l I. Each of the Venturi members 40is provided with apertures 4| at or near the point of smallest crosssection of the passage II.

The carburetor body It) is rectangular, and the air pressures existingtherein at spaced points in a given cross-sectional plane may beunequal. By the use of aplurality of hollow Venturi members 40, eachhaving spaced apertures 4|, and connecting the interiors of all theVenturi members to a common conduit 38, the pressure in the conduit 38is made to represent accurately the average pressure at the throat ofthe Venturi.

It will be seen that the pressure at the impact tubes 30 is higher thanthe pressure at the apertures 41 in the Venturi members 40, and that, inaccordance with-the well known characteristics of Venturi meters, thispressure differential is a function of the velocity of the air flowingthrough the passage H. Becauseof this pressure differential, acontinuous flow of air takes place through .of chamber 45.

scribed, so that the velocity of the air flow thru the second passage isa measure of the mass of air flowing per unit time thru the main airpassage The boost venturi 34 is provided with an annular opening 42 atits throat. Th opening 42 communicates through suitable passages with aconduit 43. In accordance with the known characteristics of Venturimeters, the pressure at the opening 42 is lower than the pressure at theopenings 4|, and the difierential between the pressure at the impacttubes 30 and the pressure at the opening 42 is a measure of air flowthrough the second air passage previously traced. It may, therefore, beseen that the boost venturi 34 provides a pressure difierential which isa measure of the mass of air flowing per unit time through the mainpassage I, but which is larger than the pressure difierential whichwould be obtained by means of a single Venturi arrangement such as theVenturi members 4!).

The pressure at the impact tubes 30 is conveyed through vent ring 3| andconduit 44 to the fuel regulating unit H. The pressure at the opening 42in the throat of boost venturi 34 is conunit 11, where these twopressures are compared in order to produce a controlling forceproportional to the difference between them.

The fuel regulator comprises a hollow cas-; ing which is divided into aseries of four expansible chambers 45, 46, 41 and 48 by means of threeflexible diaphragms 50, 5| and 52. The outer peripheries of diaphragm50, 5|, and 52 are attached to the casing of the regulator unit :withstationary valve seats 56 and 51, which may are veyed through conduit 43to the fuel regulator be formed in the casing of the regulator providedwith an hexagonal head 64 by which it may be turned to adjust thetension in the spring BI. A look nut 65 is provided to maintain the bolt53 in any position to which it may be adiusted.

The chamber 48 is connected through a passage 66 having a restriction 61therein to the interior Chamber 45 is connected through a conduit 68having a restriction 69 therein to the conduit adjacent the pressureregulator 26.

A pair of discs 10 and H are clamped,- by any suitable means, onopposite sides of a central aperture in the diaphragm 5|. Aforcetransmitting member 12 is carried by the discs 1|)- and thecarburetor per unit time.-

H and extends therethrough. The lower part of the force transmittingmember 12 is provided with a flat surface, which is adapted to engage aconvex surface at the upper end of valve member 53. Another forcetransmitting member 13 is similarly attached to the central portion ofthe diaphragm 50. The upper surface of the member 12 is recessed toreceive and cooperate with a guiding projection 14 on the lower end ofthe member 13. The upper surface of the member 13 is similarly recessedto receive and cooperate with a guiding projection 15 which is rigildlyattached to the casing of the regulator unit The amount of fuel flowingthrough the jet system 22 at any given time is a function of thepressure drop across that system. It is desired that this fuel flow beproportioned to the flow of air through the air passage As previouslydescribed, it may be seen that the pressure at the impact tubes iscommunicated through the vent ring 3| and the conduit 44 to the chamber46 in the regulator It has likewise been pointed out that the very lowpressure at th throat of the boost venturi 34 is conveyed through theconduit 43 to the interior of chamber 41. The difierence in pressuresbetween chambers 46 and 41 produces a force acting downwardly on thediaphragm 5| and the force transmitting member 12. This force is ameasure of the mass of air flowing per unit time through passage Thepressure in the chamber 48 may [be considered as being equal to, or atleast indicative of, the pressure at the intake side of the jet system22. Furthermore, the pressure in the chamber 45 is substantially equalto that existing in the conduits 68 and 25 at the discharge side of thejet system 22. The pressure in chamber 45 is less than the pressure inchamber 48 and the differential between these two pressures exertsthrough the force transmitting members 12 and 13 a force tending toclose valve member 53.

It may be stated that the differential between the pressures in thechambers 46 and 4'! exerts an opening force on the valve 53 which is afunction of the mass of air flowing through the carburetor per unit timeand that differential between the pressures in the chambers 45 and 48exerts a closing force on the valve 53, which is a function of the massof fuel flowing through The position of valve member 53 at any time isdetermined by the position it must assume to balance the force producedby the pressure differential across the jets against the force producedby the pressure differential which measures the air flow through thepassage Proper combustion conditions are attained when the mass of theair supplied to the engine is properly proportioned with respect to themass of fuel flowing, may be taken at a measure of the -mass of the fuelwithoutintroducing appreciable error.

However, the density of the air flowing through the passage varies withatmospheric pressure and with the air temperature, and hence it isnecessary in measuring the air flow to correct for variations in airtemperature and pressure in order that the metering force produced bythe chambers 46 and 41 may accurately reflect the mass of the airpassing through the passage. rather than its volume. This correction ismadeby the valve 35} whichis operated by a bellows I35 mounted withinthe housing 31'. One end of the bellows I35 is fixed to a screw I36,which threadedly engages the housing 31, so that the positions of thebellows I35 and the valve 35 with respect to the housing may beadjusted. The bellows I35 is preferably filled with nitrogen or otherinert gas. Then as the pressure in the chamber 36 varies with thealtitude of the aircraft, or from other causes,- the change in pressurecauses an expansion or contraction of bellows I35, thereby operating thevalve 35 to restrict the air flowing through the boost venturi 34 to agreater or less degree. Likewise, changes in the temperature of theflowing air cause a responsive movement of the bellows I 35' to' operatethe valve 35.

In a venturi, the difference between the pressure at the throat of theventuri and the pressure at a point upstream from the venturi isproportional to the square ofthe velocity of the fluid flowing thru theventuri. For any given venturi; this proportion only holds for a certainrange of velocities of flow. If the velocity increases beyond thisrange, the proportion no longer holds, and the pressure difference is nolonger an accurate measure of the quantity of fluid passing thru theventuri.

Whena venturi is used to measure air fio'w under conditions such asthose existing in an aircraft carburetor, the density of the air issubjectto considerable change because of temperature and pressurevariations. When the air is very thin, as at high altitudes, thevelocity of air flow past the venturi of the carburetor may increaseuntil it exceeds the limit beyond which the venturi is not accurate.

The atmospheric pressure and temperature operated valve 35 is used in myinvention to throttle the flow of fluid thru the boost venturi so as toprevent the velocity of the air flowing thru it from exceeding itslimits of accuracy. While the pressure differential between the throatof the boost venturi 34 and the vent ring 3! is not a measure of thevelocity of the fluid flowing thru the passage II because of thethrottling action of valve 35, it will be readily understood that byproperly forming the valve 35, the pressure differential referred to maybe made to accurately reflect the mass of air flowing thru the passagell. Since, in a carburetor, it is desired to proportion the mass of thefuel to the mass of the air, it will be seen that my arrangement of theboost venturi 34 and valve 35 contributes to that result, inasmuch asthe force applied to the diaphragm 5| of the regulator unit I! isthereby made proportional to the mass of the air supplied to thecarburetor.

In other words, it may be stated that by the use of valve 35, I producea flow of air thru the boost venturi 34 whose velocity is proportionalto the mass of air passing thru passage II. I then measure the velocityof the air passing thru the boost venturi by differential pressureresponsive means, and thereby secure a measurement of the mass of airsupplied to the carburetor. By using this arrangement, the velocity ofthe air flow thru the boost venturi may be always kept within the rangewhere that venturi is accurate.

The valve 35 is operated by the bellows I35 in accordance with thepressure at the throat of the large venturi. This pressure varies notonly with atmospheric pressure, but also with the velocity of the airflowing thru the carburetor.

The valve 35 therefor'eadditionally acts as a "estric'tion to maintainthe velocity of the air thru the boost venturi within the range wherethat venturi is accurate. Furthermorewhee the air flow thru the largeventuri exceeds the" limit ofthe range in which the large venturi isaccurate, the error in the pressure differential set up by the largeventuri is reflected in the pressure at its throat. This pressure,acting on valve 35 thru bellows I35, produces a corrective effect on theflow thru the boost venturi 34.

Prior devices of this type have been proposed wherein two venturis arecascaded in themain air passage so that the outlet of a smaller Veil-'-turi is located at the throat of a large venturi. The pressurediiferential between the throat of the small venturi and a pointupstream from both venturis is a measurement of the velocity of theflowing air, and this pressure differential may be corrected foratmospheric temperature and pressure to produce an indication of themass of the flowing air. In such a device, however, the small venturi issubject to the full velocity of the flowing air. Therefore, at low' airdensities and consequent high rates of flow, the device is subject tothe errors and inaccuracies inherent in the limitations of the venturi.

Since the capacity of the annular opening 4 2 in the throat of the boostventuri 34 is quite small, it is necessary that the chambers 47 and 46be separate from each other, as even a small air passage between themwould be sufli'cient to destroy the vacuum at the throat of boostventuri 34. Since the chamber 46 is in communication with the incomingair, it is possible that moisture may condense in that chamber. Henceasmall drain connection I45 is provided which connects the lowest pointin the chamber 46 with a point of relatively low pressure in the main"air passage II. It is realized that the conduit I40 is connected to apoint in the chamber 46 which appears in the drawing to be near the topof that chamber, but it should be understood that this is only forpurposes of convenience in making the: drawing and that in actualpractice the drain; tube I40 would be connected at the lowest pointinthe chamber 46. 7

Each of the vapor traps I5 and 29 consists of a chamber, such as I6 intrap I5, normally filled with fuel and having a valve 1'! in the upperportion thereof controlled by a float I8 so that the valve is closed aslong as the chamber remains filled with liquid fuel. If the fuelvaporizes, the bubbles of vapor rise to the surface of these trapswhereupon the float is lowered opening the valve so that the vapor maybe drawn offthrough the opening normally closed by the valve. Each valveis provided with a sleeve 19 which operates to close the entrance portsof the valve in case the vapor trap is inverted, such as might occurwhen the aircraft is flying upside down. The vapor trap I5 is providedwith a screen for filtering the incoming fuel.

The mixture controlling unit 2I includes a disc valve 90, which isrotatable by a shaft SI On which it is fixed. The disc valve 9!! isprovided with suitable ports so that it may be positioned to permit aflow of fuel from the conduit I9 through either a conduit 92 alone orthrough the conduit 92 and a parallel conduit 93. When the fuel isflowing through the conduit 92 only, the mixture control is said to bein the automatic lean" position, and when the fuel is flowing throughboth conduits 92 and 93, the mixture control is said to be in theautomatic rich position.

. The jet system 22 includes a pair of jets 94 and 95, both of which arein communication with the conduit 92. The jet 95 is normally closed by aspring loaded valve 96 but upon the occurrence of a sufficient pressuredifferential across the jet 95 the valve 96 is automatically opened. Theconduit 93 is connected with a jet 99. The jets 99 and 95 dischargethrough another Jet 91, and the jets 94 and 9! discharge directly intothe conduit 23.

The conduit 23 conveys the fuel to the idling control 24 which includesa jet 98. A valve member I is in the position shown in full lines in thedrawing whenever the engine is running under load. When the engine isidling the valve member I00 moves to the position shown in dotted linesin the drawing, thereby reducing the .fuel supply. The valve member I00is controlled :by a lever IOI which is connected (by means not shown) tothe mechanism which operates the throttles I02 positioned in the mainair passage I I. This idling control valve 98 cooperates with spring 6|to control the fuel flow under low air flow conditions. Under suchconditions, the air flow metering mechanism is unreliable because of thevery low flow as compared to the large cross-sectional area of the airconduit. Therefore, the spring 6| is provided to bias the valve 53 open.The valve Opening force of spring Si is opposed by the fuel pressuredifferential across the jet system tending to close the valve. Theresult is that a substantially constant fuel pressure differential ismaintained (when the air pressure differential is negligible), whosevalue is determined by the tension of spring 6|. Having such a constantfuel pressure differential, the fuel flow may then be determined by thecontour of the idle valve 98 and the throttle position. In this way, apositively controlled fuel flow is obtained under idling conditions,even though the pressure differential set up by the air venturi is smalland erratic.

The pressure regulator 26 comprises a housing divided into two chambersby a flexible diaphragm I03. A pair of discs I04 and I05 are clamped tothe central portion of the diaphragm I03, in any suitable manner. Acompression spring I06 is retained between the disc I04 and the housingof regulator 28, and biases the discs I04 and I05 for downward movement.A valve I0! is carried by the discs I04 and I05, and cooperates with aseat in the housing of regulator 26 so as to block the passage 21 whenthe valve is closed. The chamber above the diaphragm I03 is connectedthrough a passage I08 to the conduit 43, wherein the pressure isconsiderably below atmospheric. Since the pressure in conduit 25 isabove atmos pheric, it will be seen that when the engine is inoperation, the pressure differential on opposite sides of the diaphragmI03 is such as to maintain the valve I01 open, against the compressionof spring I06. The pressure in the chamber above diaphragm I03 is sosmall compared to the pressure in the chamber containing valve I 0! andthe force of the spring I06, that that small pressure exerts noappreciable controlling effect on the regulator. The low pressure abovethe diaphragm I03 does, however, provide a greater differential pressurefor opening the valve I01. The spring I06 opposes the pressure in thechamber below the diaphragm I03, and operates the valve in a manner tomaintain that pressure substantially constant.

A primary acceleration responsive regulator I I0 is shown as beingmounted on the wall of the carburetor body I 0 below the throttles I02.The regulatorl I 0 consists of a hollow casing divided into two chambersby a flexible diaphragm III. A valve stem H2 is supported centrally ofthe diaphragm III, and carries at its left hand end a valve II3. Aconduit II5 connects an annular chamber I I4 adjacent the valve stemwith the conduit I6 which is connected to the sourc of fuel underpressure. When the valve I I3 is in the position shown, it cuts off theflow of fuel from the chamber II4 into the main air passage II. Thechamber to the left of the diaphragm in the casing H0 is sealed from theannular space surrounding the valve stem H2, and is connected with themain air passage I I by means of a conduit I H. The chamber on the righthand side of diaphrgm III is connected to the main air passage IIthrough a conduit II8 having a restriction I20 therein.

As long as the air flow through the passage II remains substantiallyconstant, the pressures in the chambers on opposite sides of thediaphragm III are substantially equal, so that the valve H3 is heldclosed by the compression spring I2I. Upon a sudden opening movement ofthe throttles such as accompanies a sudden acceleration of the engine,the consequent sudden increase in pressure in the air passage II iscommunicated to the chamber at the left of diaphragm I I I more rapidlythan to the chamber at the right, because of the restriction I20.Therefore, the valve stem H2 is moved to the right against the force ofspring I21, and opens the valve II3 to provide an additional supply offuel to the engine in order that the engine may accelerate more quicklyin response to movement of the throttles.

It has been found that the additional supply of fuel provided by meansof the primary regulator I I0 may not be sufficient to accelerate theengine to the speed called for by the new throttle position. The actionof the regulator I I0 is quite rapid, and supplies an additional amountof fuel to the engine almost immediately upon opening of the throttles.This supply stops, however, as

" soon as the pressure conditions on the opposite sides of the diaphragmII I have become equalized through the restriction I20. It has beenfound with a device of this type the extra supply of fuel may be cut offbefore the engine has actually accelerated to the desired speed. Toovercome this condition there is provided a secondary accelerationresponsive regulator shown at I25 in the drawing.

The secondary regulator I25 comprises a casing divided by a flexiblediaphragm I26 into two expansible chambers. The chamber to the right ofthe diaphragm I26 is connected through a conduit I21 to a point in theair passage II downstream from the throttles I02. The diaphragm I26carries a disc valve I28 at its central portion. The valve I28 operateswith an annular seat I30, which is fixed to the body of the carburetorI0. The space inside the annular seat I30 is connected by means of aconduit I3I and a restriction I32 to the interior of chamber in the fuelregulator Il. The conduit I3I is in communication with the conduit 68through a check valve I 33. When the throttles I02 are partially closed,the pressure in the chamber to the right of diaphragm I26 is lowcompared to the fuel pressure in the chamber 45 and in the conduit 68.Therefore, at such times check valve I 39 opens. and fuel flows into thechamber at the left of diaphragm I26. The fuel is stored in thischamber. When an opening movement is given to the throttles 1 02, thepressure downstream from the throttles increases and the diaphragm I25moves to the left forcing the fuel storedin the left hand chamberthroughthe conduit l3l and restriction l32 into the chamber 45 of thefuel regulator. It will be seen that this increase in pressure in thechamber l5 has an opening effect on the fuel regulator valve 53, andthereby tends to cause the flow of an additional supply of fuel to theengine, The initiation of this increase in pressure in the chamber 45 isdelayed by the restrictions I32 and the dissipation of the increasedpressure is delayed by the restriction E9, so that the increasedpressure is maintained over a period of time considerably longer thanthat required to restore a constant pressure condition in the airpassage I l. The capacity of the secondary regulator I26 and the area ofthe restriction 132 may be so proportioned that this time delay is justsufiicient to complete the acceleration of the engine to the final speeddesired.

While I have shown and described a preferred embodiment of my invention.other modifications thereof will occur to those skilled in the art, andI therefore intend that my invention shall be limited only by theappended claims.

I claim as my invention:

1. Fluid flow measuring means, comprising in combination, a conduit forthe fluid whose flow is to be measured, first Venturi means in saidconduit, passage means havinga plurality of spaced apertures openinginto the throat of said Venturi means so that the pressure in saidpassage means is substantially equal to the average pressureat saidthroat, a second conduit connecting said passage means with a point insaid first conduit spaced from said Venturi mean-s, second Venturi meansin-said second conduit, valve means for controlling the flow of fluidthru said second conduit, means responsive to the temperature of thefluid at the entrance to said first Venturi means and to a pressuresubstantially equal to the static pressure of the flowing fluid at thethroat of said first Venturi means for operating said valve means,differential pressure measuring means, and means connecting saidmeasuring means to measure the pressure differential between the throatof said second Venturi means and said point.

2. Fluid flow measuring means, comprising in combination, a conduit forthe fluid whose flow is to be measured, first Venturi means in saidconduit for producing a pressure differential between the throat of saidVenturi means and a point in said conduit spaced from said Venturimeans, which pressure difierential is a function of the volume of fluidpassing through said Venturi means, means for amplifying saiddifferential comprising a second conduit connecting the throat of saidfirst Venturi means and said point, second Venturi means in said secondconduit, valve means in said second conduit, means responsive to thetemperature of the fluid at the entrance to said first Venturi means andto a pressure substantially equal to the static pressure of the fluid atthe throat of said first Venturi means for operating said valve means sothat the amplified pressure differential between the throat of saidsecond Venturi means and said point is substantially proportional to themass of fluid flowing thru said first-mentioned conduit.

3. A carburetor, comprising an air conduit of rectangular cross-section,first Venturi means comprising a plurality of parallel spaced hollowbars extending transversely of said conduit, each said "bar'having aplurality of spaced apertures open.-

ing into the throat of said Venturi means so that the pressure withinsaid bar is substantially equal to the average pressure at said throat,a second conduit connecting the interior of said bars with a point insaid first conduit spaced from said Venturi means, second Venturi meansin said second conduit, valve means in said second conduit,

a temperature responsive device positioned substantially centrally ofsaid first conduit ahead of said first Venturi means for operatingsaidvalve means in accordance with the temperature of the flowing air,said spaced apertures serving to 4:. A carburetor, comprising an airconduit 0f 4 rectangular cross-section, first Venturi means comprising aplurality of parallel spaced hollow bars extending transversely of saidconduit, each said bar having a plurality of spaced apertures openinginto the throat of said Venturi means so that the pressure within saidbar is substantially equal to the average pressure at said throat, ahousing positioned substantially centrally of said first conduitupstream from said first Venturi means in heat conducting relationshipwith the air flowing therethru, a sealed bellows in said housing andresponsive to the pressure therein, a first passage connecting theinteriors of said bars and the interior of saidhousing, a second passageconnecting the interior of said housing with a point in said airconduitspaced from said first Venturi means, second Venturi means insaid second passage having its discharge end closely adjacent saidhousing, a valve operated by said bellows and cooperating with saidsecond passage at the discharge end of said second Venturi means forcontrolling the flow of air from said second passage into said firstpassage, and means responsive to the difference between the pressure atsaid point in said air conduit and the :pressure at the throat of saidsecond Venturi means for controlling the flow of fuel to said-engine.

,5. A carburetor for an internal combustion engine, comprising a mainconduit for air flowing to said engine for combustion purposes, first'Venturi means in said main air conduit for creating two unequalpressures whose diiference is a measure of the velocity of the air flow,a second air conduit connecting the throat of said Venturi means with apoint in said main conduit spaced from said'Venturi means so that a flowof air thru said second conduit is induced by said unequal pressures,second Venturi means connected in series in said second air conduit, avalve in said second conduit in series with said second Venturi meansfor controlling the air flow thru said second conduit, a bellows subjectto the pressure at the throat of said first Venturi means for operatingsaid valve, an expansible chamber, a static pressure transmittingconnection between said chamber and the throat of said second Venturimeans, and means including said expansible chamber for controlling theflow of fuel to said engine.

6. A carburetor for in internal combustion engine, comprising a mainconduit for air flowing to said engine for combustion purposes, Venturimeans in said main air conduit for creating two unequal pressures whosedifference is a measure of the velocity of the air flow, a second airconduit connecting the throat of said ,Venturi means with a point insaid main conduit spaced from said Venturi means so that a flow of airthru said second conduit is induced by said unequal pressures, secondVenturi means connected in series in said second air conduit forcreating a second pressure difference varying with said velocity andgreater than said first-mentioned pressure difference, a valve in saidsecond conduit in series with said second Venturi means for modifyingthe air flow thru said second conduit, a bellows subject to the pressureat the throat of said Venturi means for operating said valve to modifysaid second pressure difference in accordance with variations in airdensity so that said second pressure difference is a measure of the massof air flowing thru said main air conduit per unit time, a pair ofexpansible chambers separated by a movable wall structure, apressure-transmitting connection between one of said chambers and saidpoint in said main conduit, a lateral opening at the throat of saidsecond Venturi means, a passage connecting said opening and the other ofsaid chambers, said passage and chamber being blind except for saidopening so that no fluid can flow into the throat of said restrictionmeans thru said opening, and means operated by movements ofsaid wallstructure for controlling the flow of fuel to said engine.

7. A carburetor for an internal combustion engine, comprising a mainconduit for air flowing to said engine for combustion purposes, firstVenturi means in said main air conduit for creating two unequalpressures whose difference is a measure of the velocity of the air flow,a second air conduit connecting the throat of said Venturi means with apoint in said main conduit spaced from said Venturi means so that a flowof air thru said second conduit is induced by said unequal pressures,second Venturi means connected in series in said second air conduit, avalve in said second conduit in series with said second Venturi meansfor controlling the air flow thru said second conduit, a bellows subjectto the pressure at the throat of said first Venturi means for operatingsaid valve, a blind passage connected to the throat of said secondVenturi means, an expansible chamber connected to said passage, andmeans including said expansible chamber for controlling the flow of fuelto said engine.

8. A carburetor, comprising an air conduit, a first Venturi structureforming a part of said conduit, a plurality of spaced apertures openinginto the throat of said Venturi structure, a passage connecting saidapertures so that the pressure within said passage is substantiallyequal to the average pressure at said throat, a housing positionedwithin said first conduit upstream from said Venturi. structure in heatconducting relationship with the air flowing therethru, a sealed bellowsin said housing and subject to the pressure therein, afluid-transmitting connection between said passage and the interior ofsaid housing, a second fluid-transmitting connection between theinterior of said housing and a point in said air conduit spaced fromsaid first Venturi means, a second Venturi structure connected in seriesin one of said connections, a valve in one of said connections operatedby said, bell ws controlling the flow of air thru said second Venturistructure, and means responsive to the difference between the pressureat said point in said air conduit and the pressure at the throat of saidsecond Venturi structure for controlling the flow of fuel to saidengine.

9. A carburetor for an internal combustion engine, comprising a mainconduit for combustion air flowing to said engine, a venturi forming apart of said conduit for producing two unequal pressures whosedifference is a measure of the velocity of air flowing thru saidconduit, a second conduit connecting the throat of said venturi with apoint in said main conduit spaced from said throat so that a flow of airis induced thru said second conduit by the difference of said pressures,said second conduit terminating at the throat of said venturi in aplurality of spaced apertures thru the walls of said throat so that thepressure at the throat end of said second conduit is substantially equalto the average pressure at said throat, a temperature responsive devicein said main conduit upstream from said venturi, said spaced aperturesserving to minimize the effects of uneven flow distribution due to thepresence of said device in the path of the flowing air, a valve formodifying the flow thru said second conduit, a connection between saiddevice and said valve for operating said valve in accordance with thetemperature of the air in said main conduit, and means responsive to therate of air flow thru said second conduit for controlling the flow offuel to said engine.

10. Apparatus for measuring the rate of flow of a fluid of variabledensity, comprising a main conduit for said fluid, a venturi forming apart of said conduit for producing two unequal pressures whosedifference is a measure of the velocity of the fluid flowing thru saidconduit, the throat of said venturi having a plurality of spacedapertures in the walls thereof a second conduit connecting the throat ofsaid venturi with a point in said main conduit spaced from said throatso that a flow of fluid is induced thru said second conduit by thedifference of said pressures, said second conduit terminating at thethroat of said venturi in said plurality of spaced apertures thru thewalls of said throat so that .the pressure at the throat end of saidsecond conduit is substantially equal to the average pressure at saidthroat, a temperature responsive device in said main conduit upstreamfrom said venturi, said spaced apertures serving to minimize the efiectsof uneven flow distribution due to the presence of said device in thepath of the flowing fluid, a valve for modifying the flow thru saidsecond conduit, a connection between said device and said valve foroperating said valve in accordance with the temperature of the fluid insaid main conduit, and means for measuring the rate of fluid flow thrusaid second conduit.

11. Apparatus for measuring the rate of flow of a fluid of variabledensity, comprising a conduit for said fluid, a first Venturi structureforming a part of said conduit, there being a plurality of spacedapertures opening into the throat of said Venturi structure, a passageconnecting said apertures so that the pressure within said passage issubstantially equal to the average pressure at said throat, a housingpositioned within said first conduit upstream from said Venturistructure in heat conducting relationship with the fluid flowingtherethru, a sealed bellows in said housing and responsive to thepressure and temperature of the fluid therein, a fluid transtrolling theiiow of fluid thru said second Venturi structure, and means formeasuring the difference between the pressure at said point in said mainconduit and the pressure at the throat of 5 said second Venturistructure.

HAROLD F. TWYMAN.

